Composites in the automotive industry

In its early days, more than a hundred years ago, an automobile was made mainly of wood and steel. Today, however, it combines a number of materials belonging to the following main families:

• ferrous materials: cast iron, steel, sheet metal (around 62% of its mass) ;

• non-ferrous materials: aluminum (cast iron and sheet metal), copper, magnesium (approx. 9%);

• mineral materials: glass, ceramics (approx. 4%) ;

• organic materials: around 25%, distributed on average as follows :

  • 4%: elastomers,

  • 6%: paints, adhesives, textiles, fluids,

  • 15%: plastic materials, thermoplastics (TP) or thermosets (TD).

Depending on the vehicle, this 15% can vary from 10 to 20% and can be distributed among the various functions that make up a vehicle as follows:

• interior equipment: 50%,

• outdoor applications: 30 to 35%,

• under-bonnet parts: 15%,

• structural parts: 0 to 5%.

It's worth noting that the percentage of plastic materials used has risen steadily since the mid-50s/60s, and was 6% in the 60s/70s.

Today, on average 15% for an average vehicle weighing 1,300 kg, this represents around 200 kg/vehicle of "plastic materials".

This evolution is due to the fact that the choice of a given material for a given application requires a confrontation of solutions in order to find the best material/process pairing for manufacturing a part, taking into account numerous criteria: technical and industrial criteria linked to the capacity and availability of industrial resources, economic criteria linked to the cost of materials and production costs, and finally social criteria guiding the choices of the end customer.

Composite materials first appeared in the automotive industry in the mid-1950s. At that time, there were few materials and processing methods available: mainly thermosetting polyester matrices reinforced with short glass fibers, processed by hand in open or closed molds using the SMC (Sheet Molding Compound) process.

Today, a wide range of materials and processing techniques are available to designers.

Matrices can be thermoplastic (polypropylene, polyamide, polyurethane,....) or thermoset (polyester, vinylester, epoxy, polydicyclopentadiene,....).

Reinforcing fibres can be made of glass, aramid, carbon, thermoplastic...